1. Technical Field
The present invention relates to a printer and a detachable printer tray.
2. Related Art
JP-A-2005-178267 (see the section “Best Mode for Carrying Out the Invention”) discloses a printer that prints on a medium like a Compact Disc-Recordable (CD-R) disc. In such a known printer that prints on a medium like a CD-R disc, the medium is placed on a tray that can be detachably mounted in the printer and the printer prints on the medium while moving the medium together with the tray.
Accordingly, in the known printer, before printing is performed, the medium placed on the tray is scanned with an optical sensor included in the printer and a center position of the medium is determined so as to adjust a print position. Therefore, an image can be printed on the medium without protruding or being displaced from the medium.
However, a threshold used in the known printer, that is, a threshold compared with a detection voltage obtained by the optical sensor to determine a detection voltage corresponding to the medium is set to a constant value in advance. Therefore, depending on the sensitivity of the optical sensor that differs for each printer, there is a risk that it will be difficult to detect the accurate position and the like of the medium.
For example, if the threshold largely differs from the middle value between the detection voltage obtained by the optical sensor at the medium and the detection voltage obtained by the optical sensor at the tray and the like and is close to one of the two detection voltages, the following problems will occur. That is, the printer will discriminate the medium from other objects with the threshold at a position where the voltage does not change suddenly in a detection voltage waveform obtained in the scanning process using the optical sensor. As a result, if the detection voltage waveform obtained in the scanning process using the optical sensor is influenced by noise, an area and a position of the medium determined on the basis of the threshold will vary, even when the noise level is low. Therefore, the reliability of the detected position of the medium is reduced and a print displacement easily occurs.
In addition, if the threshold is substantially equal to the detection voltage obtained by the optical sensor at the medium or the detection voltage obtained by the optical sensor at the tray and the like, it becomes difficult for the printer to recognize the medium with the threshold. As a result, it becomes difficult for the printer to adequately print on the medium.
Therefore, expensive sensors with uniform quality that have small differences in the sensitivity thereof or sensors having sensitivities within a predetermined range are used as the optical sensor for determining the position and the like of the medium on the tray.